Magneto-Electric Rotation Detector Frequently Asked Questions

Operating principle of MP-981

The MP-981 Magneto-Electric Rotation Detector incorporates magnetic resistance elements, permanent magnets, a DC amplifier, and a voltage regulator to measure the rotation speed of gears from ultra-low to high speeds (1 to 20 kHz).

The MP-981 has a detection part equipped with magnetoresistive elements at the sensor tip. This detection part consists of two magnetoresistive elements, MR1 and MR2, and a magnet. By shaping the signal waveform detected by this detection part, the MP-981 obtains a rectangular wave output.

circuit block diagram

The detection unit consists of two magnetoresistive elements, MR1 and MR2, and a magnet, as shown in the figure below. The magnetoresistive elements exhibit a resistance value that is proportional to the magnitude of the applied magnetic field. When a magnetic object (gear) is present in front of the sensor, the strength of the magnetic field changes. Therefore, if the position of the magnetic object is unbalanced with respect to each magnetoresistive element, the resistance values will also be unbalanced. By applying a constant voltage between terminals 1 and 3 and observing the output voltage at terminal 2, the output signal from terminal 2 changes in a manner that traces the shape of the gear.

The signal obtained from the magnetoresistive sensor is shaped into a waveform to produce the final signal. Since the signal amplitude from the magnetoresistive sensor is small (tens of mV), changes in midpoint voltage due to temperature variations or increases in rotation speed can lead to changes in duty cycle or loss of pulse output.